1. Field of the Invention
The invention is generally related to pipeline connections and more particularly to branch pipeline connections that allow a pig to be passed through a pipeline.
2. General Background
For marine pipelines, it is sometimes necessary to move a cleaning or inspection tool commonly known in the industry as a "pig" through the entire length of the pipeline. The need may occur upon completion of the pipeline before it is put into service or after the pipeline has been in service for a period of time.
A marine pipeline system may consist of a number of branch or tributary pipelines feeding product into a common main or trunkline. When it is necessary to pump an intelligent or "smart" pig downstream through a branch line, special considerations in the design of the trunkline-branch connection are necessary. One of the special considerations is inclusion of a "piggable-Y" branch connection in the trunkline to allow the "smart" pig to pass unimpeded from the branch pipeline into the trunkline.
The design arrangement of the piggable-Y in the trunkline will impact the methods of installation of the trunkline portion containing the piggable-Y. The present state-of-the-art technology for design of trunkline piggable-Y connections does not allow for the most direct and low cost installation method; installing the piggable-Y directly in the trunkline during pipe laying of the trunkline.
Particularly for pipe laying operations on the bottom of a body of water, pipeline branch assemblies present a unique set of problems that are interrelated between the insertion and removal of pigs, the pipe laying operation itself, and the installation of the branch connections. These problems involve limitations on the type of pigs that may be used, the limitations and requirements for pipe laying equipment, and the need for the use of divers. These problems will be discussed further in the detailed description with reference to drawings to more clearly illustrate the problems involved.
The present state of the art does not address these problems and leaves a need for pipeline branch connections that are less restrictive on the type of pigs that may be used, the pipe laying operation, and the need for divers.